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          <i class="fa fa-codepen fa-lg"></i> Edit
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        <div class="span12">
          <h4 id="title">Raster Source</h4>
          <p class="tags">
            <span class="badge-group">
              <a
                href="./index.html?q=raster" class="badge badge-info">raster</a
              ><a
                class="badge badge-info tag-modal-toggle text-white"
                data-toggle="modal"
                data-target="#tag-example-list"
                data-title="raster"
                data-content="
                  &lt;a class=&quot;list-group-item list-group-item-action active&quot; href=&quot;./raster.html&quot;&gt;Raster Source&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./region-growing.html&quot;&gt;Region Growing&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./sea-level.html&quot;&gt;Sea Level&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./shaded-relief.html&quot;&gt;Shaded Relief&lt;/a&gt;"
                tabindex="0"
                >4</a>
            </span>
            <span class="badge-group">
              <a
                href="./index.html?q=pixel" class="badge badge-info">pixel</a
              ><a
                class="badge badge-info tag-modal-toggle text-white"
                data-toggle="modal"
                data-target="#tag-example-list"
                data-title="pixel"
                data-content="
                  &lt;a class=&quot;list-group-item list-group-item-action active&quot; href=&quot;./raster.html&quot;&gt;Raster Source&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./zoomify.html&quot;&gt;Zoomify&lt;/a&gt;"
                tabindex="0"
                >2</a>
            </span>
            <span class="badge-group">
              <a
                href="./index.html?q=maptiler" class="badge badge-info">maptiler</a
              ><a
                class="badge badge-info tag-modal-toggle text-white"
                data-toggle="modal"
                data-target="#tag-example-list"
                data-title="maptiler"
                data-content="
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./zoom-constrained.html&quot;&gt;Constrained Zoom&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./drag-and-drop.html&quot;&gt;Drag-and-Drop&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./drag-and-drop-image-vector.html&quot;&gt;Drag-and-Drop Image Vector&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./full-screen.html&quot;&gt;Full Screen Control&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./full-screen-drag-rotate-and-zoom.html&quot;&gt;Full Screen Drag, Rotate, and Zoom&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./gpx.html&quot;&gt;GPX Data&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./image-filter.html&quot;&gt;Image Filters&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./interpolation.html&quot;&gt;Interpolation&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./kml.html&quot;&gt;KML&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./layer-spy.html&quot;&gt;Layer Spy&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./layer-swipe.html&quot;&gt;Layer Swipe&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./magnify.html&quot;&gt;Magnify&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./mapbox-layer.html&quot;&gt;Mapbox-gl Layer&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./feature-move-animation.html&quot;&gt;Marker Animation&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./vector-osm.html&quot;&gt;OSM XML&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action active&quot; href=&quot;./raster.html&quot;&gt;Raster Source&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./region-growing.html&quot;&gt;Region Growing&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./side-by-side.html&quot;&gt;Shared Views&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./street-labels.html&quot;&gt;Street Labels&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./mapbox-style.html&quot;&gt;Vector tiles created from a Mapbox Style object&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./vector-tiles-4326.html&quot;&gt;Vector tiles in EPSG:4326&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./vector-wfs.html&quot;&gt;WFS&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./vector-wfs-getfeature.html&quot;&gt;WFS - GetFeature&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./vector-wfs-geographic.html&quot;&gt;WFS with geographic coordinates&lt;/a&gt;
                  &lt;a class=&quot;list-group-item list-group-item-action&quot; href=&quot;./xyz-retina.html&quot;&gt;XYZ Retina Tiles&lt;/a&gt;"
                tabindex="0"
                >25</a>
            </span>
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  <div id="map" class="map"></div>
  <div id="plot"></div>
</div>

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        <form method="POST" id="codepen-form" target="_blank" action="https://codesandbox.io/api/v1/sandboxes/define">
          <input id="codesandbox-params" type="hidden" name="parameters">
        </form>
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      <div class="row-fluid">
        <div class="span12">
          <p id="shortdesc">Demonstrates pixelwise operations with a raster source.</p>
          <div id="docs"><p>
  This example uses a <code>ol/source/Raster</code> to generate data
  based on another source.  The raster source accepts any number of
  input sources (tile or image based) and runs a pipeline of
  operations on the input pixels.  The return from the final
  operation is used as the data for the output source.
</p> <p>
  In this case, a single tiled source of imagery is used as input.
  For each pixel, the Vegetation Greenness Index
  (<a href="https://www.tandfonline.com/doi/abs/10.1080/10106040108542184#.Vb90ITBViko">VGI</a>)
  is calculated from the input pixels.  A second operation colors
  those pixels based on a threshold value (values above the
  threshold are green and those below are transparent).
</p>
</div>
        </div>
      </div>

      <div class="row-fluid">
        <h5 class="source-heading">main.js</h5>
        <pre><code id="example-js-source" class="language-js">import 'ol/ol.css';
import Map from &#x27;ol/Map&#x27;;
import RasterSource from &#x27;ol/source/Raster&#x27;;
import View from &#x27;ol/View&#x27;;
import XYZ from &#x27;ol/source/XYZ&#x27;;
import {Image as ImageLayer, Tile as TileLayer} from &#x27;ol/layer&#x27;;

const minVgi &#x3D; 0;
const maxVgi &#x3D; 0.5;
const bins &#x3D; 10;

/**
 * Calculate the Vegetation Greenness Index (VGI) from an input pixel.  This
 * is a rough estimate assuming that pixel values correspond to reflectance.
 * @param {Array&lt;number&gt;} pixel An array of [R, G, B, A] values.
 * @return {number} The VGI value for the given pixel.
 */
function vgi(pixel) {
  const r &#x3D; pixel[0] / 255;
  const g &#x3D; pixel[1] / 255;
  const b &#x3D; pixel[2] / 255;
  return (2 * g - r - b) / (2 * g + r + b);
}

/**
 * Summarize values for a histogram.
 * @param {numver} value A VGI value.
 * @param {Object} counts An object for keeping track of VGI counts.
 */
function summarize(value, counts) {
  const min &#x3D; counts.min;
  const max &#x3D; counts.max;
  const num &#x3D; counts.values.length;
  if (value &lt; min) {
    // do nothing
  } else if (value &gt;&#x3D; max) {
    counts.values[num - 1] +&#x3D; 1;
  } else {
    const index &#x3D; Math.floor((value - min) / counts.delta);
    counts.values[index] +&#x3D; 1;
  }
}

/**
 * Use aerial imagery as the input data for the raster source.
 */

const key &#x3D; &#x27;Get your own API key at https://www.maptiler.com/cloud/&#x27;;
const attributions &#x3D;
  &#x27;&lt;a href&#x3D;&quot;https://www.maptiler.com/copyright/&quot; target&#x3D;&quot;_blank&quot;&gt;&amp;copy; MapTiler&lt;/a&gt; &#x27; +
  &#x27;&lt;a href&#x3D;&quot;https://www.openstreetmap.org/copyright&quot; target&#x3D;&quot;_blank&quot;&gt;&amp;copy; OpenStreetMap contributors&lt;/a&gt;&#x27;;

const aerial &#x3D; new XYZ({
  attributions: attributions,
  url: &#x27;https://api.maptiler.com/tiles/satellite/{z}/{x}/{y}.jpg?key&#x3D;&#x27; + key,
  maxZoom: 20,
  crossOrigin: &#x27;&#x27;,
});

/**
 * Create a raster source where pixels with VGI values above a threshold will
 * be colored green.
 */
const raster &#x3D; new RasterSource({
  sources: [aerial],
  /**
   * Run calculations on pixel data.
   * @param {Array} pixels List of pixels (one per source).
   * @param {Object} data User data object.
   * @return {Array} The output pixel.
   */
  operation: function (pixels, data) {
    const pixel &#x3D; pixels[0];
    const value &#x3D; vgi(pixel);
    summarize(value, data.counts);
    if (value &gt;&#x3D; data.threshold) {
      pixel[0] &#x3D; 0;
      pixel[1] &#x3D; 255;
      pixel[2] &#x3D; 0;
      pixel[3] &#x3D; 128;
    } else {
      pixel[3] &#x3D; 0;
    }
    return pixel;
  },
  lib: {
    vgi: vgi,
    summarize: summarize,
  },
});
raster.set(&#x27;threshold&#x27;, 0.25);

function createCounts(min, max, num) {
  const values &#x3D; new Array(num);
  for (let i &#x3D; 0; i &lt; num; ++i) {
    values[i] &#x3D; 0;
  }
  return {
    min: min,
    max: max,
    values: values,
    delta: (max - min) / num,
  };
}

raster.on(&#x27;beforeoperations&#x27;, function (event) {
  event.data.counts &#x3D; createCounts(minVgi, maxVgi, bins);
  event.data.threshold &#x3D; raster.get(&#x27;threshold&#x27;);
});

raster.on(&#x27;afteroperations&#x27;, function (event) {
  schedulePlot(event.resolution, event.data.counts, event.data.threshold);
});

const map &#x3D; new Map({
  layers: [
    new TileLayer({
      source: aerial,
    }),
    new ImageLayer({
      source: raster,
    }),
  ],
  target: &#x27;map&#x27;,
  view: new View({
    center: [-9651695, 4937351],
    zoom: 13,
    minZoom: 12,
    maxZoom: 19,
  }),
});

let timer &#x3D; null;
function schedulePlot(resolution, counts, threshold) {
  if (timer) {
    clearTimeout(timer);
    timer &#x3D; null;
  }
  timer &#x3D; setTimeout(plot.bind(null, resolution, counts, threshold), 1000 / 60);
}

const barWidth &#x3D; 15;
const plotHeight &#x3D; 150;
const chart &#x3D; d3
  .select(&#x27;#plot&#x27;)
  .append(&#x27;svg&#x27;)
  .attr(&#x27;width&#x27;, barWidth * bins)
  .attr(&#x27;height&#x27;, plotHeight);

const chartRect &#x3D; chart.node().getBoundingClientRect();

const tip &#x3D; d3.select(document.body).append(&#x27;div&#x27;).attr(&#x27;class&#x27;, &#x27;tip&#x27;);

function plot(resolution, counts, threshold) {
  const yScale &#x3D; d3
    .scaleLinear()
    .domain([0, d3.max(counts.values)])
    .range([0, plotHeight]);

  const bar &#x3D; chart.selectAll(&#x27;rect&#x27;).data(counts.values);

  bar.enter().append(&#x27;rect&#x27;);

  bar
    .attr(&#x27;class&#x27;, function (count, index) {
      const value &#x3D; counts.min + index * counts.delta;
      return &#x27;bar&#x27; + (value &gt;&#x3D; threshold ? &#x27; selected&#x27; : &#x27;&#x27;);
    })
    .attr(&#x27;width&#x27;, barWidth - 2);

  bar
    .transition()
    .attr(&#x27;transform&#x27;, function (value, index) {
      return (
        &#x27;translate(&#x27; +
        index * barWidth +
        &#x27;, &#x27; +
        (plotHeight - yScale(value)) +
        &#x27;)&#x27;
      );
    })
    .attr(&#x27;height&#x27;, yScale);

  bar.on(&#x27;mousemove&#x27;, function () {
    const index &#x3D; bar.nodes().indexOf(this);
    const threshold &#x3D; counts.min + index * counts.delta;
    if (raster.get(&#x27;threshold&#x27;) !&#x3D;&#x3D; threshold) {
      raster.set(&#x27;threshold&#x27;, threshold);
      raster.changed();
    }
  });

  bar.on(&#x27;mouseover&#x27;, function (event) {
    const index &#x3D; bar.nodes().indexOf(this);
    let area &#x3D; 0;
    for (let i &#x3D; counts.values.length - 1; i &gt;&#x3D; index; --i) {
      area +&#x3D; resolution * resolution * counts.values[i];
    }
    tip.html(message(counts.min + index * counts.delta, area));
    tip.style(&#x27;display&#x27;, &#x27;block&#x27;);
    tip
      .transition()
      .style(&#x27;left&#x27;, chartRect.left + index * barWidth + barWidth / 2 + &#x27;px&#x27;)
      .style(&#x27;top&#x27;, event.y - 60 + &#x27;px&#x27;)
      .style(&#x27;opacity&#x27;, 1);
  });

  bar.on(&#x27;mouseout&#x27;, function () {
    tip
      .transition()
      .style(&#x27;opacity&#x27;, 0)
      .on(&#x27;end&#x27;, function () {
        tip.style(&#x27;display&#x27;, &#x27;none&#x27;);
      });
  });
}

function message(value, area) {
  const acres &#x3D; (area / 4046.86)
    .toFixed(0)
    .replace(/\B(?&#x3D;(\d{3})+(?!\d))/g, &#x27;,&#x27;);
  return acres + &#x27; acres at&lt;br&gt;&#x27; + value.toFixed(2) + &#x27; VGI or above&#x27;;
}
</code></pre>
      </div>

      <div class="row-fluid">
        <h5 class="source-heading">index.html</h5>
        <pre><code id="example-html-source" class="language-markup">&lt;!DOCTYPE html&gt;
&lt;html lang="en"&gt;
  &lt;head&gt;
    &lt;meta charset="UTF-8"&gt;
    &lt;title&gt;Raster Source&lt;/title&gt;
    &lt;!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer --&gt;
    &lt;script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"&gt;&lt;/script&gt;
    &lt;!-- The lines below are only needed for old environments like Internet Explorer and Android 4.x --&gt;
    &lt;script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,TextDecoder"&gt;&lt;/script&gt;
    &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"&gt;&lt;/script&gt;
    &lt;script src&#x3D;&quot;https://unpkg.com/d3@6.7.0/dist/d3.min.js&quot;&gt;&lt;/script&gt;
    &lt;style&gt;
      .map {
        width: 100%;
        height:400px;
      }
      .rel {
        position: relative
      }

      #plot {
        pointer-events: none;
        position: absolute;
        bottom: 10px;
        left: 10px;
      }

      .bar {
        pointer-events: auto;
        fill: #AFAFB9;
      }

      .bar.selected {
        fill: green;
      }

      .tip {
        position: absolute;
        background: black;
        color: white;
        padding: 6px;
        font-size: 12px;
        border-radius: 4px;
        margin-bottom: 10px;
        display: none;
        opacity: 0;
      }
    &lt;/style&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;div class&#x3D;&quot;rel&quot;&gt;
      &lt;div id&#x3D;&quot;map&quot; class&#x3D;&quot;map&quot;&gt;&lt;/div&gt;
      &lt;div id&#x3D;&quot;plot&quot;&gt;&lt;/div&gt;
    &lt;/div&gt;
    &lt;script src="main.js"&gt;&lt;/script&gt;
  &lt;/body&gt;
&lt;/html&gt;</code></pre>
      </div>

      <div class="row-fluid">
        <h5 class="source-heading">package.json</h5>
        <pre><code id="example-pkg-source" class="language-json">{
  &quot;name&quot;: &quot;raster&quot;,
  &quot;dependencies&quot;: {
    &quot;ol&quot;: &quot;6.13.0&quot;
  },
  &quot;devDependencies&quot;: {
    &quot;parcel&quot;: &quot;^2.0.0&quot;
  },
  &quot;scripts&quot;: {
    &quot;start&quot;: &quot;parcel index.html&quot;,
    &quot;build&quot;: &quot;parcel build --public-url . index.html&quot;
  }
}</code></pre>
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